Using GPS to Measure Precipitable Water Vapor in Antarctica

Amanda MurrayGeorgia State University

TAMDEF GPS Receivers in Antarctica

GPS signal delays

• GPS is broadcast on

the L1 and L2 signals

• Precipitable Water

Vapor (PWV) can be

extracted from the

signal delay

www.redorbit.com/modules/reflib/article_images/21_aab02a40d790b5bdb771c2f0fd2fc6d0.jpgwww.trimble.com/gps/howgps-error.shtml

Ionosphere

http://web.mit.edu/jync/www/layers.gif

Atmospheric Mesoscale Prediction System

• At present, a reliable source for predictions• Predicts model data for multiple variables• Makes predictions every 6 hours

• 2-meter temperature (k)• Surface pressure (hPa)• Moisture (mm)

Map Making

• AMPS data downloaded for 2005

• Variables geocoded to 30km x 30km grid

• 4500 maps for each variable

Temperature Moisture Pressure

Animation for Moisture

Interpolation – the beginningStar – GPS site

Latitude point80° south

This is a small slice of Southern

Victoria Land.

Interpolation• Latitudes for each GPS site used

• Extracted values from each variable for GPS sitesMoisture Temperature Pressure

Time Series – moisture (coastal)

Time Series – Moisture (mixed)

Calculations

• ZHD = 2.2779*(Ps/(1-0.00266*COS(2λ)-0.00028*H))

• λ = latitude in radians

• H = height of GPS site above the ellipsoid in km

• Ps = surface pressure in hPa

• ZWD = ZPD - ZHD

• PW = П * ZWD

Differences (at each GPS site)

• Acquired ZPDs for 23 of 31 GPS sites

• Observations taken every 2 hours

• Each site has different number of observations

• Matched up ZPDs to variables

Zenith Neutral Delays – Time Series

Zenith Wet Delays

Problems & Solutions• Possibly using 2 different ellipsoids• Pressure values could be inaccurate• Zenith Neutral Delays could be of bad quality

• Find out if model values are on a topographical model or ellipsoidal model

• Interpolate model ‘elevations’ and compare to actual height above ellipsoid

• Use interpolated values (if correct) in ZHD equation

Importance?

• More accurate weather forecasts

• Improve current climate models

• Contribute to studies of climate change

• Further insight into any ongoing climate change in Antarctica

Questions?

I would like to thank Dr. Mike Willis for working with me, Dr. Terry Wilson for letting me be a part of her project, Kelly Carroll for his help and support, everyone involved with OSU SROP and especially NSF and POLENET for making this opportunity available.

Thank you!